The pulmonary and systemic arterial pressure wave is an important parameter in the diagnosis of various pulmonary artery and systemic artery diseases such as pulmonary hypertension, pulmonary stenosis, systemic hypertension and arterial stenosis. Invasive methods of pressure measurement cause discomfort for the patients, and they include procedural and post-operative risks, the later including infection with an increasing incidence of mortality due to antibiotic resistant bacteria. Accordingly, non-invasive techniques for blood pressure measurement are preferred and may become increasingly important.
Once such technique is known as applanation tonometry. However, it is limited to measurement in certain locations such as the radial arteries at wrist or carotid arteries where these systemic arteries are close to the surface of the skin. Moreover, commercially-available tonometric devices are all quite motion-sensitive further limiting their use/applicability. Still further: affixing, wearing and ultimately removing the force or displacement sensor employed a tonometric monitoring system can be difficult and sometimes uncomfortable.
Another technique for estimating blood pressure is variously described in which blood velocity is measured via ultrasound Doppler and then the Bernoulli equation applied to calculate a result. However, the Bernoulli equation does not properly apply to moving boundary condition systems or those involving unsteady flow—both of which are features of the relevant biological systems. As such, the accuracy/applicability of these approaches are limited. These methods can only provide estimates for mean pressure, systolic pressure, and/or diastolic pressure. They are not able to provide the pressure wave or pressure at any time during a cardiac cycle.
Therefore, improved noninvasive techniques—especially noncontact methods—for measuring and/or monitoring the arterial pressure waveform are needed.